Researchers show for the first time that a mammal begins to suckle its mother's milk through a learned response built on learning her unique combination of smells. When it is born, the newborn is exposed to the smell of its mother's amniotic fluid and the baby then responds to those smells to feed. Prevailing thought has been that pheromones –chemicals that trigger an innate behaviour – drove the suckling response as an automatic behaviour. The new work determines that, in mice, the smells must be learned before the behaviour can occur. Suckling is a critical step for survival in mammals, which are defined by giving birth to offspring that need to feed from their mother's milk. The newborn must begin to feed soon after birth or it will die. It is a crucial, defining behaviour in mammals and offers researchers an opportunity to investigate the biology of instinct.